Logs, lumber, and other forms of wood are susceptible to attack by a variety of destructive insects, larvae, and fungi including: Subterranean, Dampwood, and Drywood termites; wood boring beetles; carpenter ants; and fungi such as Poria sp., Polyporous sp., Coniophora cerebella, C. putriana, Lenzitis sapiara, L. tribium, Merulius lacrymans, Poxillus sp., Xestobium rufivollosum, Anobium punctatum, A. mollis, and Callidum viollacem. Other partial lists of insects and fungi that cause wood damage can be found in BORA-CARE.TM., Termiticide Insecticide and Fungicide Concentrate and in U.S. Borax Service Bulletin & Specimen Label 200.
There are many treatment agents and application techniques designed to protect wood against attack by the foregoing and other insects and fungi. The compounds commonly used for such treatment agents comprise an active ingredient which actually kills the insects, fungi, etc., and a carrier which functions to carry the active ingredient into the wood by diffusion. A commonly used active ingredient is a boron composition such as disodium octoborate tetrahydrate (DOT), marketed under the trademark TIMBOR. Commonly, such a boron compound is provided: (1) in an aqueous carrier; (2) in a liquid carrier and penetration aid such as a mixture of ethylene glycol and water (U.S. Pat. No. 4,610,881 issued 9 September 1986 to Bechgaard) or a mixture of polyethylene and ethylene glycols (U.S. Pat. No. 5,104,664 issued 14 April 1992 to Palmere et al.); or (3) in a microcrystalline formulation which is subsequently diluted with water and used as a dip or spray (U.S. Pat. No. 5,129,946 issued 14 July 1992 to Evans and Treatment of Log-Home Logs with Thickened Boron, Puettmann et al., 42 Forest Products Journal 11/12, November/December 1992, pp 30-32).
The foregoing, and similar, products have significant drawbacks. Those which contain ethylene glycol are unsafe (ethylene glycol is classified as a toxic chemical). The active principles in boron-based products with an aqueous carrier do not diffuse well into dry wood. Water evaporates too quickly for it to transport the active ingredient to the center of a wooden component of significant thickness.
Available alternatives to the boron-based wood preservatives discussed above are fumigants, pesticides, and pressure treatment formulations which contain CCA (chromated copper arsenate) and other toxic compounds containing copper, chromium, or arsenic. Pressure treated logs are also unpopular as the preservative turns the wood green. Or, if a stain is added to the formulation, it gives what is regarded by some as an unnatural appearance which is incompatible with the desired look of log homes.
As will be apparent to the reader, there is a continuing and present need for an improved way of protecting woods against attack by destructive insects and fungi.